Re: NULLs
Date: Wed, 26 Dec 2007 23:17:52 -0400
Message-ID: <47731962$0$5286$9a566e8b_at_news.aliant.net>
stevedtrm wrote:
> On 26 Dec, 17:47, "David Cressey" <cresse..._at_verizon.net> wrote:
>
>>"stevedtrm" <steved..._at_hotmail.com> wrote in message
>>
>>news:4afba236-4273-4d24-b8f4-5041483d22fc_at_i12g2000prf.googlegroups.com...
>>
>>
>>>What are NULLs for?
>>
>>>Missing information? Then surely there should just be no tuple?
>>
>>>To indicate that there can be no value? Why not a seperate table with
>>>a boolean value in the non-key column?
>>
>>>Steve B.
>>
>>Go to google groups. Select the newsgroup comp.databases.theory
>>
>>Do a search on NULLS. You will find a multitude of discussions about NULLS.
>>almost everything that this discussion might produce has been said in at
>>least one of those discussions.
>>
>>Short answer: yes, it is to indicate that there is no value.
>
>
> OK.
>
> A brief perusal of those discussions gives me no reason to think NULLS
> are necessary.
>
> Furthermore, they reflect some sort of internal Codd/Date debate as to
> how to handle NULLs. Something about 2nd and 3rd order logic (my
> mathematics is too rusty to get anything more than an instinctive
> grasp of this)
That's 2-valued logic versus 3-valued logic not 1st order logic versus 2nd order logic, which is a whole other discussion.
> What were the two positions, hypersummarised?
There are more than 2 positions. SQL introduced NULL as a very hackish kludge. Codd pointed out that a single NULL marker did not suffice and suggested 2 markers. Date pointed out that one can apply the same argument to 2 markers leading to an infinite progression once one heads down that path, which suggests the path was never a productive one to head down in the first place.
> If everyone is clear NULLS shouldnt be used, why the debate as to what
> to do about them ?
Because SQL allows NULL and even promotes the idea that NULL solves some problem instead of introducing many. Received on Thu Dec 27 2007 - 04:17:52 CET